Seed meters for dispensing seeds at a controlled rate into a seed furrow as the seed meter is advanced above and along the seed furrow have been in use for many years. In a conventional arrangement, a tractor is coupled with planting units with seed meters. The planting units generally include seed hoppers for the seeds to be planted or a smaller container fed from a centralized bin or large hopper, and a device for opening a furrow in the ground as the tractor is advanced across the field. A seed meter is connected to the seed hopper for dispensing individual seeds into the furrow at a controlled rate, and a further device for moving soil at the sides of the furrow to close the furrow over the seeds.
The tractor may move across the field at speeds of about 4 to about 8 miles per hour with spacing between the planting of seeds ranging from as little as 0.5 inches or less to as much as 10 inches or more depending upon the particular seed being planted. A seed metering mechanism must therefore be able to dispense the seeds at various rates depending on the desired spacing. In addition to being able to dispense seeds at different rates, seed meters must also account for differences in the size, shape and surfaces of seeds.
One type of seed meter is a mechanical type meter. Typical mechanical seed meters are generally limited as to the speed at which they operate and are not suitable for handling different types of seeds without cumbersome equipment changes.
Other seed meters have utilized air pressure differential, such as a vacuum to overcome some of the problems of the mechanical seed meters. Vacuum seed meters typically utilize a vacuum source coupled to a chamber on the opposite side of the seed disc from the seed hopper with the vacuum communicating through the apertures in the seed disc to the seeds.
One problem that occasionally arises with vacuum seed meters is an untimely disengagement of the seed or complete failure to disengage the seed from the aperture. This is often due to the fact that a relatively strong vacuum that is typically required to provide a sufficient pressure differential to hold the seeds within the apertures within the disc. The presence of a strong vacuum force also results in greater rotational friction of the seed meter, which requires greater workforce to operate. Smaller seeds or portions of larger seeds occasionally become lodged in the disc openings and are not timely released or released at all at the discharge area of the seed metering mechanism.
Various approaches have been used to address this problem. In U.S. Pat. No. 5,740,747, a vibration apparatus is utilized to shake the seeds from the apertures. In U.S. Pat. No. 5,170,909 a lower power vacuum is utilized with the assistance of an agitator and seed accelerator in the seed mass. Seeds are released by cutting the vacuum source from the seed. It would be desirable to provide a vacuum seed metering mechanism wherein the release of seeds from the disc is positively affected and the seeds are readily and reliably discharged from the seed metering disc and mechanism without the need for such complicated related mechanisms.